The present invention relates to a linear aromatic polyester copolymer having a heat resistance and a process for the preparation thereof.
Aromatic polyester resins consisting of aromatic dicarboxylic acids and bivalent phenolic compounds have been known from old times. Various processes for preparing the aromatic polyester resins are also known, e.g. a process by an interfacial polymerization in which an aromatic dicarboxylic acid chloride dissolved in an organic solvent immiscible with water and a bisphenol compound dissolved in an aqueous alkali solution are mixed and reacted (as disclosed in Japanese Patent Publication No. 1959/1965), a process by solution polymerization in which an aromatic dicarboxylic acid chloride and a bisphenol compound are reacted in an organic solvent (as disclosed in Japanese Patent Publication No. 5599/1962), and a process by ester interchange in which an aromatic dicarboxylic acid phenyl ester and a bisphenol compound are heated (as disclosed in Japanese Patent Publication Nos. 15247/1963 and 28119/1968). In the polymers so prepared, for instance, a polymer of 2,2-bis(4-hydroxyphenyl)propane as a bisphenol component and terephthalic acid as an aromatic dicarboxylic acid component is a crystalline polymer and is slightly soluble in an organic solvent, and accordingly the use has been attended with difficulty, despite of having an excellent heat resistance, i.e. melting point of 350.degree. C. In order to eliminate this defect, it is proposed to impart flexural portions into the polymer molecule by employing isophthalic acid as one of dicarboxylic acid components so as to produce a substantially amorphous polymer. This modification is useful in its own way, but has the disadvantages that isophthalic acid must be employed in as small amount as possible when an excellent heat resistance is desired, and the degree of crystallinity increases with the decrease of the amount.